Variable electrical condenser



Patented De.24, 1940 '2,225,855

UNITED. STATI-:s PATENT OFFICE VARIABLE. ELECTRICAL coNDENsER Sidney George Brown, London, England, assignor to The Telegraph Condenser Company Limited, North ActonEngland, a British company Application January 17, 1939, Serial No. 251,418 In Great Britain January 19, 1938 2 Claims. (Cl. F75-41.5)

The prese-nt invention relates to electrical conand connection to an externalv circuit may be densers of the type wherein the capacity is varimade by soldering a wire thereto, by means of able by virtue of the fact that one of v the eleca screw terminal or in any other suitable manner trodes of the condenser is movable in relation notv shown. The electrode 2 is a sliding fit in 5 to the other. Such variable condensersareoften its groove 4, `thus permitting its rotation whereby 5f employed for the tuning of a wireless set or for its convolutions may be interlaced in varying trimming purposes, that is to say, for providing degree with those of the electrode I, thus proa means of effecting a small adjustment in a total viding the desired adjustability of electrical cacapacity mainly constituted by a larger conpacity. To effect electrical connection from the ,i

l0 denser. movable electrode 2 to an external circuit, a metal l0' An object of the invention is the'production of spring 6 bears on the periphery of the electrode. avariable electrical condenser comprising in com- In the case of the aboveedescribed construcbination an electrode formed as a helix and a tion of condenser, it isevident that, in order that second electrode also formed as a co-axial helix it may be adjusted to its minimum capacity, that l Y whereof the convolutions lie between those of is when there is no rinterlacing between the 1 5rl said first-mentioned helix, said electrodes being helices, the effective length is at least'twice that relatively rotatable about their common axis of one helix; this may be regarded as a diswhereby their degree of interlacing may be varied. advantage, which is avoided in the construction Another object of the invention .is the proaccording to the present inventiondepict'ed in 2e vision of a variable electrical condenser wherein Figures 2, 3 and 4.

the construction comprises a stem of insulating This form of condenser comprises a base 'I of material having at least two helical grooves in ceramic material, Bakelite or othersuitable inits periphery and an electrode located in and sulating substance, provided with a central stem projecting radially from each of said grooves, 8 having two helical grooves 9, I 0 of unequal at least certain of said electrodes being rotatable depth. In the shallower groove 9 the fixed elec- 25 relatively to each other about said stem. trode II is located and the electrode I2, rela- A further object of the invention is the contively movable, occupies the deeper groove ID. struction of a variable electrical condenser as Extending through the stem 8, there is a spindle in the preceding paragraph having a metal spin- I3, of conducting material, having a shoulder I4,

.10 dle rotatable within the said stem to which the a iiange I5 and a head I6 formed with a saw cut 30 movable electrode or electrodes is or are attached I1 to facilitate rotation of the spindle, At its and whereby adjustment of the capacity is efopposite end, the spindle I3 has a peripheral fected. groove I8, engaged by the forked end I9 of a Other objects and advantages of the invention metal arm 2l! fixed to the base I by a rivet 2|;

will appear from the following description, which axial movement of the spindle is thus prevented, 35 includes reference to the accompanying drawing, while it is free to rotate in the stem 8. One end wherein: of the movable electrode I2 is attached at 22 to Figure 1 illustrates the essential features of a the flange I5, whereby, on rotation of the spindle condenser having interlacing helical electrodes, I3, the degree with which the electrode I2 is inas already known, terlaced with the electrode II, is varied. 40

Figure 2 is aplan view, In Figure 3 the electrodes are shown as fully Figure 3 1s asectionalvlew, and interlaced, providing maximum capacity, while Figure 4 is an outside elevation of a preferred in Figure 4 they are depicted as completely disform of construction according to the present engaged, resulting in minimum capacity; in the invention. latter position, on account of the above-described 45 Referring to Figure l, the electrodes of the mechanism, the electrode I2 is compressed so condenser comprise metal strips wound edgewise .that the distance between its convolutions is reto constitute two helices I, 2; alternatively these duced or even eliminated. When the spindle I3 helices might be of insulating material coated is rotated from the position of minimum capacity with an electrically conducting substance. The shown in Figure 4 in such a direction as to in- 50 electrodes are respectively supported in helical crease the capacity, the end of the electrode I2 grooves 3, 4 formed in the surface of a central enters the deeper groove I0 designed for it and insulating stem 5, conveniently made of ceramic therefore remains correctly spaced from the elecmaterial, Bakelite or any other appropriate introde II. Attached to the latter is a soldering sulator. The electrode I is fixed in its groove 3 tag 23 iixed to the base I by a rivet 24, while con- 55 nection to the movable electrode I2 is eil'ected by a tag 25 held by the rivet 2|. Movement of the electrode l2 may be limited by a stop 26 and a similar stop may be provided for locating the electrode Il.

In the condensers illustrated variation of capacity is substantially proportional to the degree of rotation of the movable electrode. If desired, however, the width of the strip may be varied in any desired manner to form, for instance, a tapered coil or helix, or any other desired shape, thereby enabling the increase or decrease of capacity to vary in any predetermined manner. Alternatively, the pitch of the screw thread may be varied along its length if desired, to form any predetermined variation of capacity to the turns of one element in relation to the other.

The invention is susceptible of many structural variations. For instance, if desired, the elements may be so arranged that the periphery of the convolutions is caused to engage within an internal thread of a housing instead, as previously described, upon a central stem. In some cases it may be desirable and convenient to dispense with the threaded stem or housing in which case the spacing between the coils or convolutions could be maintained by the addition of suitable insulators attached thereto.

In the constructions described above there are two spiral elements, one fixed and the other movable, but it will be apparent that more than two elements can be used and the number of iixed elements and movable elements arranged as desired.

In the drawing, the variable electrical condenser is shown as a single unit, but in some cases, for instance, for use in a wireless receiver, it is often convenient to arrange several such condensers in one unit. In this case the base l could be extended and the threaded stems added as required.

Each of the helical electrodes may be produced as an end-on shaving cut from a solid bar or tube of a suitable conducting material. The requisite thickness of the said helical shaving may be readily secured by a suitable feed of the cutter in relation to the number of revolutions of the bar or the like from which -the helix is to be cut. Of course, if desired, the section of the said shaving may be varied to meet requirements; for instance, the cutter may be so shaped as to produce a corrugated shaving or a curved form.

What I claim and desire to secure by Letters Patent of the United States is:

1. A variable electrical condenser, comprising in combination a stem of insulating material having two helical grooves in its periphery, a conducting spindle rotatable within said stem, an electrode located in and projecting radially from each of said grooves, one of said electrodes being movable around said stem and mechanically connected with said spindle and the other of said electrodes being xed relatively to said stem, said spindle having a peripheral groove, and an arm fixed at one end relatively to the stern and at its other end having a fork having operative engagement in said groove.

2. A variable electrical condenser, comprising a stem of insulation material having two helical grooves in its periphery, a current conducting spindle rotatable in and extending through said stem, a helical electrode located in and projecting radially from each of said grooves, one of said electrodes being movable around said stem, a flange around an end of said spindle and spaced from ythe adjacent end of said stem, and said movable electrode being attached at one end to said liange and being drawn into the space between the flange and the said end of the stem when the spindle is turned in one direction, the

other electrode being fixed relatively to the stem.

SIDNEY GEORGE BROWN. 

